The Browse retrieve facets endpoint lists all the customer-defined facets present in the current index, while the retrieve facet options (values) by facet name and retrieve facets with their options (values) endpoints indicates all the facet options (values) available for a given facet group (key), along with counts for the number of items available for each.
This can be useful to validate the integrity of a catalog by checking the number of products present for each brand, or within each group (category) as well as to power facet listings for web interfaces.
The Browse retrieve facets endpoint can be used with production-level loads. Given customers may potentially define thousands of facets, the full list of facets is sorted ascending alphabetically, and paginated. This endpoint does not return individual item results - for this purpose reference the standard Browse retrieve by filter name/value endpoint.